Rapid advances in communication, digital processing, and computing systems are creating an increasing demand for nonvolatile random access memory that is both high-density and highspeed. Existing solid-state technologies are unable to provide all of the needed attributes in a single memory solution. Therefore, a number of different memories are currently being used to achieve the multiple functionality requirements, often compromising performance and adding cost to the system. Magnetoresistive random access memory (MRAM) technology is known in the art. MRAMs use principles of magnetoresistive tunneling. Digital bits of information are defined by memory cells having alternate states of magnetization of magnetic materials. The magnetic materials can be thin ferromagnetic films. High-quality, nanometer scale tunneling barriers can be used that have enhanced magnetoresistive response.
Information can be stored and retrieved from the memory devices by inductive sensing to determine a magnetization state of the devices, or by magnetoresistive sensing of the magnetization states of the memory devices. It is noted that the term “magnetoresistive” characterizes the device and not the access method—a magnetoresistive device can be accessed by, for example, either inductive sensing or magnetoresistive sensing methodologies.
A significant amount of research is currently being invested in magnetic digital memories, such as, for example, MRAMs, because such memories are seen to have significant potential advantages relative to the dynamic random access memory (DRAM) components and static random access memory (SRAM) components that are presently in widespread use. For instance, a problem with DRAM is that it relies on power storage within capacitors. Such capacitors leak energy, and must be refreshed at intervals. The constant refreshing of DRAM devices can drain energy from batteries utilized to power the devices, and can lead to problems with lost data since information stored in the DRAM devices is lost when power to the devices is shut down.
SRAM devices can avoid some of the problems associated with DRAM devices, in that SRAM devices do not require constant refreshing. Further, SRAM devices are typically faster than DRAM devices. However, SRAM devices take up more semiconductor real estate than do DRAM devices. As continuing efforts are made to increase the density of memory devices, semiconductor real estate becomes increasingly valuable. Accordingly, SRAM technologies are difficult to incorporate as standard memory devices in memory arrays.
MRAM devices have the potential to alleviate the problems associated with DRAM devices and SRAM devices. Specifically, MRAM devices do not require constant refreshing, but instead store data in stable magnetic states. Further, the data stored in MRAM devices can potentially remain within the devices even if power to the devices is shutdown or lost. Additionally, MRAM devices can potentially be formed to utilize less than or equal to the amount of semiconductor real estate associated with DRAM devices, and can accordingly potentially be more economical to incorporate into large memory arrays than are SRAM devices. MRAMs are nonvolatile, and operate at high-speeds. They also have substantially unlimited read and write endurance.
Although MRAM devices have potential to be utilized as digital memory devices, they are currently not widely utilized. Several problems associated with MRAM technologies remain to be addressed. It would be desirable to develop improved MRAM devices.
Integrated circuit sensors are known in the art. For example, U.S. Pat. No. 6,180,989 to Bryant et al. (incorporated herein by reference) discloses an integrated circuit fingerprint sensor.
U.S. Pat. No. 4,674,319 to Muller et al. (incorporated herein by reference) relates to an integrated circuit sensor for vapor detection. A polysilicon microstructure is formed on a silicon substrate. Beneath the microstructure are diffused regions in the substrate. The microstructure is capacitively coupled to diffused regions so that one capacitor acts as an excitation capacitor and another capacitor acts as a sense capacitor. When an AC voltage is applied to the excitation capacitor, the electrostatic force between the substrate and the microstructure changes, causing a mechanical vibration in the microstructure. A DC voltage is applied to the sense capacitor. The mechanical vibration changes the capacitance of the sense capacitor and will develop a current through the sense capacitor. A phenomenon may then be sensed by the vibrating microstructure.
U.S. Pat. No. 6,194,961 to Passeraub (incorporated herein by reference) relates to a microstructure including an electronic circuit formed by a plurality of transistors and a flat coil. The coil is arranged on an upper face of a semiconductor substrate. The coil generates a magnetic field in this substrate in the vicinity of the transistors. The transistors are situated in superposition with the coil. The source and collector of the transistors are aligned along a direction perpendicular to the wire or path in the portion of the coil situated in proximity to each of the transistors. Thus, electric current flowing in the transistors is substantially parallel to the magnetic field.
U.S. Pat. No. 6,263,740 to Sridhar et al. (incorporated herein by reference) relates to a pressure sensor fabricated onto a substrate using conventional CMOS fabrication processes.
However, these integrated circuit sensors do not sense environmental information that may affect operation of the integrated circuit itself.